In general, motion such as tool path and revolutions per minute is numerically controlled, and as a result, a machine tool performs a cutting process of a workpiece. Examples of a machine tool include a machining center, a turning center, an NC milling machine, and the like. The machine tool is also referred to as a numerically controlled composite machine.
The tool includes a rotating cutting tool that performs a cutting process on a workpiece which is rotated and stopped while being mounted on a spindle. Examples of the rotating cutting tool include an end mill, a milling tool, a drilling tool, a boring tool, and the like. Hereinafter, the “rotating cutting tool” is abbreviated as the “tool”.
It is evaluated that productivity of the machine tool is good as material removal rate (MRR) per time is higher and it is evaluated that a processing grade is good as surface roughness of a processing surface is smooth.
A cutting volume per time is determined according to cutting parameters such as a radial depth of cut, an axial depth of cut, main axis revolutions per minute, and a feed rate. If any one of the cutting parameters is increased, the cutting volume is increased. However, when vibration chatter occurs in spite of improved productivity, the processing grade may deteriorate.
Accordingly, an optimal cutting condition needs to be set in order to satisfy both productivity improvement and the processing grade.
Meanwhile, there is a case that a cutting condition of the tool is presented as a manual recommended by a tool manufacturer. However, the cutting condition recommended as a manual by tool manufacturer is just provided based on a maximum allowable static processing load and is not provided based on a chatter vibration characteristic which occurs during a cutting process
Accordingly, there is a problem in that it is impossible to handle breakages of the tool and the workpiece under chatter vibration which occurs during the cutting process and a dynamic processing load amplified through the chatter vibration. As a result, a worker tends to perform the cutting process by setting a much more stable cutting condition than the manual recommendation condition.
The aforementioned chatter vibration is characterized in that the chatter vibration is consistently varied due to a lot of causes such as a tool type, a tool shape, a tool overhang length, hardness of the work, a processing position (X, Y, and Z coordinate positions), and the like.
That is, since the worker applies a very conservative cutting condition among the manual recommendation conditions presented by the tool manufacturer, the productivity deteriorates.
On the other hand, when the cutting process is started, it is very difficult to change a value of a depth of cut particularly axial depth of cut while the cutting process is performed. That is, when the cutting process is performed by incorrectly setting an initial depth of cut in the cutting process, the depth of cut cannot be corrected easily while the cutting process is performed, and as a result, since there is a concern that the processing grade of the workpiece is lowered or the productivity deteriorates, it is very important to set an initial axial depth of cut.